Variable valve actuation (VVA) systems are well known in the automotive arts for improving performance of internal combustion engines. Some known VVA systems employ a motor-driven actuator rod, also referred to herein as a “bi-directional actuator”, for varying the contact position of a cam follower on an engine cam lobe. The present invention applies to actuator systems for variable valvetrains which experience an average drive torque favoring rotation of the bi-directional actuator in one direction and hindering rotation in the opposing direction. The present invention provides a means to optimally bias the average torque of a bi-directional drive actuator system toward zero. Thus, the present invention helps to provide more equal response time in either direction of rotation as well as to reduce the overall motor requirements for the system by reducing the overall peak-to-peak torque variation.
A mechanism which can provide a constant torque bias is not the optimal solution because it merely shifts the torque signature and does not change the overall peak-to-peak value.
What is needed in the art is a mechanism for compensating systematic uni-directional torque bias imposed on a bi-directional drive actuator shaft wherein the compensating bias torque is non-linear over the rotational range of authority of the actuator shaft and is desirably equal and opposite to the systematic torque differences.
It is a principal object of the present invention to help to balance the mechanism torques and reduce the overall peak-to-peak torque variation.
It is a further object of the invention to provide a significant benefit on packaging, assembly, and overall system cost.